1. Field of the Invention
The present invention relates to a coating method and a coating apparatus of spraying a liquid paint from a rotary atomizing head and thus performing an electrostatic coating.
2. Related Art
As a coating apparatus of coating a body of an automobile and the like, a rotary atomization coating apparatus has been known. In the rotary atomization coating apparatus, a high voltage is applied to a rotary atomizing head that is rotating, and at this state, a conductive paint (liquid paint) is supplied to the rotating rotary atomizing head. Thereby, the liquid paint is electrified and atomized and is then sprayed from a front end edge of the rotary atomizing head, so that an electrostatic coating is performed.
Regarding the rotary atomization coating apparatus, JP-A-60-054754 discloses that air injecting ports for pattern deformation are provided only at upper and lower parts or left and right parts so as to remove lowering of a coating efficiency or deviation of a coating film thickness due to a coating pattern having a doughnut shape, a coating pattern is deformed to an elliptical shape by air for pattern deformation and a coating film thickness is thus made to be uniform.
However, in the elliptical coating pattern, upper, lower, left and right coating areas are different. When the coating is performed in the upper-lower direction, and when the coating is performed in the left-right direction, the coating film thickness is not the same. Therefore, moving (teaching) of a coating gun for uniformly recoating a coating pattern is highly limited.
Also, it is considered to remove the doughnut shape by increasing an inclined angle of annular shaping air to a direction of a rotational shaft, compared to a usual case. In this case, however, a diameter of the coating pattern is decreased, so that the coating efficiency is lowered. Also, an air ring that is a member for injecting the shaping air is enlarged, so that a robot operation is restricted.
JP-A-2009-072703 discloses that an amount of air injection from an air injecting port is controlled so as to securely apply paint to a work (object to be painted) having a complicated shape, thereby changing a coating pattern diameter.
In the coating by the rotary atomization coating apparatus, the paint is generally sprayed with the coating gun being perpendicular to a part to be painted of the work, i.e., a rotational axis of a rotary atomizing head configuring the coating gun being arranged to be substantially perpendicular to the part to be painted, considering the coating efficiency.
However, when coating an inner plate and the like of an automobile, the coating may be performed with the coating gun being obliquely arranged relative to the part to be painted, not perpendicularly thereto, so as to avoid an interference of the coating gun with the work. In this case, since the recoating is performed using an end portion of a coating pattern having a small amount of coating, the coating efficiency is lowered.